Vapor recovery system for fuel tanks



June 2, 1953 s. c. DOELTER 2,640,627

VAPOR RECOVERY SYSTEM F OR FUEL TANKS Filed Jan. 14, 1950 B5 OLJQJA.

ATTORNEBS Patented June 2, 1 953 VAPOR RECOVERY SYSTEM FOR FUEL TANKS Gandolph C. Doelter, Paris, France, assignor to Vadolt Trust, Vaduz, Principality of Liechtenstein, a company of the Principality of Liechtenstein Application January 14, 1950, Serial No. 138,692 In Switzerland January 15, 1949 1 Claim.

The present invention relates to a process and a device for condensing fuel vapours, especially those of aviation petrol, formed during flight at great altitudes.

' Boiling and excessive vapour formation in highly volatile fuels, especially aviation fuels, occur when aircraft reach considerable altitudes of flight. The cause of this phenomenon is to be found in the lowering of the boiling point of the fuel in relation to that obtaining at ground level (flying altitude zero), this lowering of the boiling point being itself due to the progressive decrease in atmospheric pressure that accompanies an increase of altitude. The attainment of this lower boiling point is, however, also substantially influenced by the temperature of the fuel, which latter cannot, with the high climbing speeds of modern aircraft, cool at the rate that would be necessary to compensate for the rapid fall in atmospheric pressure and thereby keep the boiling point to some extent within the limits obtaining at ground level.

A high climbing speed of the aircraft, and a high ground temperature of the fuel, both unfavourably influence the shift of boiling point and consequently the formation of vapour, quite apart from the quality of the fuel. By quality, in this connection, should be understood the proportion of extremely volatile components of particularly low boiling point. An aviation fuel, for instance, that commences to boil at approximately 62 C. at a ground-level temperature of 27 C. and a flying altitude of zero will boil at a flying altitude of 8200 metres if it has retained its ground-level temperature of 27 C. At an.

altitude of 12,000 metres the same fuel would need to be cooled to 8 C. to be just below boiling point, and at 15,000 metres it would have to be cooled to 6 C.

The climbing speeds of modern jet-propelled fighter aircraft (approximately 3000 metres per minute), for instance, permit, in the short times involved, of no appreciable cooling of the supply of fuel carried. The consequence is excessive boiling of the fuel in the tank, which leads to substantial losses of fuel, quite apart from complications arising in other directions, and the vapours formed are forced through the venting pipe of the tank into the outer atmosphere and lost. The most obvious solution to this problem, namely, to prevent escape of the vapours by hermetically sealing the tank, would call for tanks of high resistance to internal pressure, and would, for reasons of weight and safety, not be'feasible, especially in view of the danger of explosion that would arise in the the aircraft coming under fire.

This formation of vapour has itself a powerful cooling action on the fuel. The high heat requirements of the evaporation process resultassuming that adiabatic cooling takes placein so much heat being extracted from the fuel that its temperature constantly falls. Moreover, the chemical composition of the boiling fuel changes, as the more volatile components evaporate first.

Even allowing for the compensatory action'of the cooling process, the losses caused by boiling amount, by the time a flying altitude of 1500 metres is attained, and assuming a ground-level temperature of 27 C. of the fuel, to approximately 12% of the liquid volume. At higher ground-level temperatures in summer or under tropical conditions the losses by evaporation may reach as much as 18%.

In order to overcome, in actual flying operations, the difiiculties arising from the phenomena described, the following fundamental measures have hitherto been available:

(a) The use of a fuel of particularly low vapour pressure, i. e., high boiling point. This solution to the problem is, however, universally impracticable with the existing production plant and the existing designs of aircraft engines.

event of Another possibility is to use low-volatile crude petrol or diesel oil for driving gas turbines, but this involves complications both of an operationa1 nature and in the matter of supplies.

(b) Cooling the fuel before taking off or during flight. Pre-cooling of the fuel before taking off is technically feasible, but it complicates the refuelling arrangements and interferes with the take-01f of the aircraft, which in the case'for instance of fighter aircraft, cannot often be accurately predetermined as to time. A travelling ground refrigerator plant for this purpose would have to be driven by a motor of approximately hp. to cool the entire fuel load of a twin-engined jet-propelled bomber from 30 C. to 0 C. in half an hour.

Cooling during flight, especially cooling of the entire supply of fuel, is not possible in practice'- except perhaps in the case of non-self-sealing metal wing tanks and low climbing speedsas the installation of the necessary coolers and circulation pumps would be associated with enormous drawbacks from the point of view of weight and of streamlining. A twin-engined jet-propelled bomber, for instance, would require, under summer conditions, to cool its fuel supply,

a cooler having a front surface area of at least 0.55 square metre, and the entire supply of fuel would have to be pumped through once per minute.

(c) The-use of vhigh-pressure:tanksiis, as already indicated, i ln'db iuniversa'lly practicable for reasons of weight and safety.

The object of the process in accordance with the present invention is not to prevent the boiling of the fuel, but deliberately to encompass such boiling and consequently to keep it under control at all times. The inventiveprocessmom sists in creating in a tank,,.by.exhaustingzthewm pours from the tank by meanszof a1pump,ra;pressure inferior to that of the outside atmosphere, thus causing the fuel to boilearlier .than under normal conditions in compressing the vapours so withdrawn and returning them to thet'ank'in a liquid state.

The cooler and pump are therefore dimensioned .to cope. with .smallquantities of vapourtonly; the actual cooling of the fueltta-kes .placaautornati- .cally nsiairesult of theextraetion-zof.heattdurin g ahoiling. :Byccontrolling Ithe time 1 taken =to =reach Lbciling point, .-i. e... by regulating the 'intakersuc- ,tionof -.the .condenser tpump and thereby the ire- ;tluc-tionzof ither-pressureiinthe tank, the boiling: of lithe firel'cambe intentionallyproducedrataltitudes Llowenthan til-4381352111) which. ittwouldiothemvisetaire ,place. The @substantial fquantities -.of heat :use

for the evaporating process promote rapid iand learlvacooling of -the .f.uel, which hasa :"compen'sastory effect Font-the boilingpointwhen greater. alti- Itud'es of fiight'arerattained,11.12., -when a: further iiallfoftpressure-inthettankoccurs.

Evaporation will nonsequently :he kept almost aiconstanttat alltimesfiand-reven: atimaximumi alti- -.tudes of =flie'htzand maximum climbing. speeds-win not exceed ithedappropriately calculated capacity of the condenser pump. mlreinegative apressure .producedinithe tankby the suctional-evacuation .-.of ithe vapours .is--.maintained :by suitable. means within .the :rangewf 120 to 805mm. mercury gauge and consequently doesinot influence the-strength requirements oithettank. The supply ofi'fresh air .-to*=the tan-kitalces:place-lautomaticallyionlydmprctpor-tionr-ito the volumaof ,ifueltpumped to -.the cengine.

.Evaporation losses are :in this way .entirely eliminated. .ApreliminaryLconditionrfor thiszconolensation of vapour, =-and-self'-.eooling, is .the use .ofaexisting delivery tpumps capable of handling even boilingiuel.

The device .used to .perform .the ,pmeess loomiprises in accordance withtheinvention, aicomhined' suction and force, pump that is connected on thetonethand by aisuctiompipe -to.the upperimost pant sof -thki11tGTiGT -.of -the tank. and .suc- ,tionallyiexhaustsvand compressestthe vapour from ithevtank, anddelivers .it via .-a=.cooling devicein iwhichitis-condensed, tothe liquid-fuel. The delliverytpipeextendsrto-the top .of .the tankand is surroundedzbyiapipe.openatthebottomand providedat its upper-extremitywith gas outlet: apertures in such a way that the cooled fuel is'added .to: andmi'xed with .the contents of .the tank .from below and .entrained ,gases escapeLthrough said apertures. into .theupper portion of the tank, the .suction and delivery ,pipes .both being .provided with valves. .The. figure .of .the ..drawing shows a diagrammaticside elevation view ottheinvention. L Ihe annexed.drawingillustrates a typicalembo'climentof the inventive device .comprising .the following -vloasic..functiona1 units: .the condenser pump 1, .which suctionally removes via .the vent pipe 4, and compresses, the fuel vapours 15a formed in the tank; the cooler 8, which gives 01? the heat released by the compression and condensation of the fuel vapours in the pump; the baro- .metric regulating valve-9, vwhiclhmaintains the :necessary mondcnsing ,pressure in pump and cooler; and the barometric regulating valve 5, the purpose of which is to keep the pressure in the tank at all times about 20 to 30 mm. mercury gauge helow the outer atmospheric pressure as soon as the pump starts up.

The=diagramshown in the drawing relates to a device of -atype that can be used for fuel tanks iipreferabi-yaccommodated in the wings of an aircraft. The wing'rl, shown in cross-section, contains the fuel tank 2 with a filler hole 3. The feed i pump l3 forces'th'efuel i2 through the pipe M to the engine. The vapours a formed in the tan'kaabove the surface of the fuel and produced by the boiling of the highly volatile fuel during xfiightJat-high altitudestaressuctionallyWithdrawn t-t'hroughthe pipe-4 .by the pump J. ilheJatter compresses :the vapours and pauses them to -condense. The power required to efi'ect .this com- ,pression -.is supplied .-.-by the ,pump .motor sand is converted .into the :heat liberated :by -.the .cone- .densed. vapours, .this heat .beingtgiven .off by -.the .c0o1er-.8. Theicooled-and condensed, liquid lfuel returns to the -..tank via the delivery valve 8 "through .the misery-pipe .HJ. Thezriser ,pipe ill reitztends almost .to time topnf .the tankand -is-.surdioundedtbymhe.separatorttube 'H, which is-open at its loweriextremity. .Thepurpose of .this pipe H .isvtomixthe liquidemerging-fromthe pipe Jfl with-the remaining zliquid contentsptthe ttank under conditionsof minimum vapourzandzbnbble iormation, :this .llllXiIlg being efiected wia tthe opening-attirebottomzofsaid pipe 1H. .-A plural iitytofiopenings rill-provided at .the upper .endto'f .said pipe a, ll buttbelow the outlet aperturemf'the ,r-iser ,-.pipe H1, serve -:the ipurposeiof conducting to a point above the surface..of-.-the liquidinzthe-tank the vapour or. air e'buhblesdnevitably; entrained or formed. thus,- preventing. their bubblingsup through -.the.liq uid.

lllhe regulating valve 5 comprising two parts, has a twofold .-funct-icn. sWhen -.the -,pump ii is operating, .the valve ?5 (required =totensure that -the negative ,pressure created in the space by the. suctional withdrawal-.ofithe vapouradoes not fall below the eexternal atmospheric pressure .-.by more ,than. a icertainamount, usually "2040 mm. mercury gauge. lfthasuctionoflthe pump '1 ex- :ceeds .what :is :necessary to :cope with the :guan- .ti ty -.of vapour formed, i.-.e.,iifathetnegativepres- T'sure'passes .beyond-themange specified, theinlet malve-openssoas .to adjustrthe negative pressure .in .relation .to vthe :external atmosphere {pressure until the negative pressure set is-restored. .-If,,0n .the-other hand, theiformation-of vapour for any reason-assumes proportions. exceeding the-capacity of -.the pump, .or ii-for instance, the .pump -is not functioning, .the vapour-s formed are, .aszsoon as .the negative .pressurahas reached a'rvalueofflo to 30 mm. "mercury gauge, .allowed -.by the I outlet .valve to.esca.pe.into the outenatmosphere .via the {pipe 6 and the aperture Hi, this being -.accomplishrgdbytheregulating valve .5.

This .arrangement ensures .-that negative or ,positive pressures ,ofmore than .20 110. 30 mm. mercury .gauge .helow or above .the ,prevailing external atmospheric pressure .canneverarise-in the tank. When .the pump is functioning, i.-.e., when the vapours are being .suctionally withdrawn thereisalways.a.slightnegativepressure in the tank, this being of particular advantage when the tank is slightly damaged.

The further valves and safety devices necessary are omitted from the drawing to avoid confusion.

I claim:

A device for condensing fuel vapours, the device comprising a tank, a combined suction and force pump for the vapours in the tank, a suction pipe connecting the pump to the uppermost part of the interior of the tank; the device further comprising a delivery pipe and a cooling device and a separator pipe, the pump being connected to the delivery pipe through the cooling device, the delivery pip returning the fuel from the cooling device in which the vapour is condensed to the tank, the delivery pipe entering at the bottom of the tank and extending upwar-dly therein substantially to the top thereof, the delivery pipe being substantially surrounded in the tank by the separator pipe, the separator pipe being open at the lower end thereof and having at least one apertur formed therein adjacent the upper end extremity, and a valve connected to the suction pipe.

GANDOLPH C. DOELTER.

References Cited in the file ofthis patent UNITED STATES PATENTS Number Name Date 1,439,451 Seibert et a1 Dec. 19, 1922 1,808,618 Trezise June 2, 1931 2,059,942 Gibson Nov. 3, 1936 2,126,367 Clawson et al Aug. 9, 1938 2,379,215 Brinkmann June 26, 1945 

